Electrothermal actuator



1965 J. F. SHERWOOD ELECTROTHERMAL ACTUATOR Filed Oct. 7, 1963 R O T N E V W 23 John E Sherwood ATTORN5 United States Patent 0 ice 3,166,893 ELETROTHERIQIAL ACTUATGl-l Joint F. Sherwood, 75% W. 39th Ave, Wheat Ridge, Colo. Filed Get. '7, 1963, Ser. No. 314,143 9 Claims. (Cl. oil-23) This invention relates to an actuator and more particularly to an eleetrotliermal actuator which comprises a reciprocable shaft for imparting motion to other mechanism, such, for example, as valves, dampers, and the lil:

illectrotiicrmal actuators are small devices, usually having an outer diameter of one inch or less. Due to the small size of such actuators it has been d' ficult to find an electric switch small enough to fit within the housing, dependable in operation and not exhorbitantly high in cost. When, as heretofore, a switch is located laterally the shaft, the shape of the housing may be asymmetrical or it must be no y enlarged to contain the conventional thermal motor parts and the switch.

One object of the invention is to provide housing which is symmetrical and which compactly encloses a reciprocable shaft, slratt seals and bearing, and an electrical switch for controlling the operation of the shaft, all arranged in axial alignment.

Electrotbermal actuators employ a shaft which has a ,oiston or force-receiving end portion located in a high pressure chamber containing expansible and contractibl material for actuating the shaft. The opposite end of the shaft is a work-contacting 'ree end adapted to actuate other mechanism located externally of the actuator, heating of the expansiole material being controlled by an electrical switcli. A11 object of my invention is to provide means located between the ends of such a reciprocable slzaft for exerting annular bearing pressure and direct axial iilitlSi. on the switch mechanism to open the switch contact points without interfering with the worl contacting function of the free end of the sliaft.

Another object of the invention is to provide a novel shaft construction which enables me to utilize shafts of uniform size and length for different actuator installations, which can be purchased economically in quantity, including means easily applied to such shafts to vary their lengths as required for different installations and to increase the shaft strength.

Another object of the invention is to provide such shaft length varying means in the form of an elongated cap having an annular flange thereon adjacent its open end. Such a cap can be applied to a shaft to increase its axial length and to increase the diameter of the work-contacting end portion of the shaft as desired; and, further, the annular flange on the cap provides a thrust surface for actuating the switch mechanism of my invention. Due to the location of the flange between the ends of the sliaft, and the arrangement of the switch mechanism which permits the reciprocable shaft to extend through and beyond the said mechanism before the flange contacts the switch mechanism, the work-contacting end of the shaft is free to perform its intended function. When shaft has reached the end of its predetermined stroke, the switch mechanism is actuated by the flange on the cap to open the switch contacts and thus cut off electrical current to the heating element in the high pressure chamber.

In addition to utilizing the shaft cap for carrying the switch actuating means and for varying the length of the shaft to which it is applied, my shaft construction has other advantages. Since the shaft is a highly precisioned product, adjustments necessary to control the shaft strolze can be made on the cap which does not have to be precisione The addition of the cap also lengthens tire stroke capabilities of the shaft resulting in economics bea a? a,iili9, tiff; ?c.tenteol Jan. 26, i965 cause a shorter length shaft can be used. Further, the addition of the cap strengthens the work contacting end of the shaft and eliminates the need for deforming the shaft to provide switch actuating means as has been the custom when a switch was located laterally of the shaft. Still further, the presence of the switch actuating means on the inner end of the shaft cap serves as a stop for limiting the re in stroke of the shaft without employing grooves or deforming means on the shaft for that purpose.

Other objects and advantages of the invention will be the drawings and following specification.

2 dr" ngs:

l is a longitudinal vertical sectional view, partly in elevation, of a thermal actuator embodying the reciprocated shaft and electrical switch of my invention, taken in the planes of the lines 11 of FIG. 3, showing the shaft in retracted position and the switch contacts closed.

HQ: 2 is a view similar to FIG. 1, showing a part of the actuator, with. the shaft in extended position and the switch contacts open.

3 is an elevational end View of the actuator with switch housing end plate removed and the shaft in section.

FIG. 4 is eievational view of a modified form of shaft, showing part of the switch mechanism in section.

in that embodiment of the invention shown in the drawtags, the thermal actuator it is of the type shown in my Patent No. 3,029,595 and comprises a high pressure housing WlEiCll encloses a chamber 12 containing expansible contractible material such as wax or other suitable for imparting motion to a shaft. An elect ical heating element 1 is connected to electrodes 14 mounted in insulating seals 15 in one end 16 or thehousing 11. Connected to the other end of die housing is a shaft bearing housing 17 provided with bores of dilferent diameters for having mounted therein a reclprocated shaft Zil and shaft bearing and seals. The shaft 26 comprises a piston portion 21 extending into the chamber 12 and an opposite free work portion 22. on which is mounted an elon ated cap 23 having a 24 on its inner The shaft 28 is mounted in a piston seal 25, lubricant 26 and lubricant seal J7 which are the subject of my co-pe ding applic tion, Serial No. 295,003, and therefore need not be descr ed in detail herein. Assembly of tire housings ll 17 firmly con .fmes the seals and shaft bearings, botn axially and radially.

The; portion of the housing 17 adjacent the lubricant seal 27 has a shaft receiving bore adapted to slidably receive the shaft 29, said bore being smaller in diameter than the bore 2%, thus forming a shoulder which serves as a stop for the fanged end 2d of tlie capped shaft. The presence of the portion 23 of the housing between the flanged end 24 of the shaft cap and the lubricant seal 27 serves to confine the seal, limits the return stroke of the shaft, and prevents the shaft cap flange from bearing on the seal 2'7.

The end 351 of the housing 17 is larger in diameter than the housing to form a switch chamber closed by an end plate 32. The switch chamber is proportioned to receive an electrical switch mounted concentrically with the shaft Eli and constructed to receive direct axial thrust for actuation of the switch mechanism. The housing 31 also encloses the end of the conduit 33 encasing the electrical wiring 54 bet een the switch and th electrodes 14.

The switch 35 comprises a flat bottom base 36 of insulating material, provided with a central opening 37 and peripheral recesses which accommodate the conduit 33 and mounting screws 38, 39. The base 36 is thickened by a blade supporting portion ill located on the upper posite the point 43 is provided with a hole 45 for attachment of the electrical wiring 34. A movable contact blade 46, as a whole, is fastened by rivets 47 to the blade supporting portion it? of the base. Said blade at comprises a pair of parallel spring metal arms 48 connected together at one end by the curved cross member 42 with apertured extension 5%), and at the opposite end by the converging portions 51 of the arms 48 carrying the depending contact point 52 at their junction. Extending inwardly from the junction of the portions 51 is a eaf spring 53. The blade 46 is mounted on the base portion 49 of the base in such position that the contact 52 registers with the fixed contact 43. Between the base 36 and blade 46, above the recess at, is a floating disc 55 of insulating material, cut away at one side ss. The disc is provided with a central aperture 57 smaller in diameter than the opening 37 in the base and concentric with said opening. The floating disc 55 has 21 depending peripheral flange 58 for seating in the recess 41. The central hole 57 communicates with a slot 59 extending to the cut away side edge 56. A rib (it) extends diametrically across the top of the floating disc 55.

A retainer ear comprises a base 651 and upturned car 62 provided with a groove 63 which extends across the face of the ear for reception of the end of the leaf spring 53. The ear base 61 is fastened to the switch base by rivet 64.

An upper stop comprises a base as with prongs as for fastening the stop on the base 36 in such position that the flat top member 67 overlies the arms 51 above the movable contact 52.

When the described parts are mounted on the base 36,

. the floating disc 55 rests loosely on the base, with the my invention is as follows: When the switch contact points 43 and 52 are closed, as shown in FIG. 1, electrical current heats the expansible material in the chamber 12; expansion of the material causes the shaft 29 to move outwardly until the flange 24 exerts thrust in axial direction against the annular surface 68 on the floating disc 55 of the switch, as shown in FIG. 2, causing the switch blade 46 and contact point 52 thereon to separate from the fixed contact to break the circuit. Before this occurs, the shaft 26 will have reached its work-contacting position to impart motion to mechanism (not shown) located externally of the actuator. Opening of the contacts results in cooling and contraction of the material in the high pressure chamber 12, whereupon the shaft 20 returns to the position shown in FIG. 1, for repetition of the cycle of movements. The leaf spring 53 causes closing of the contact points by snap action when the flange on the shaft cap moves away from the switch mechanism on the return stroke of the shaft. It will be understood that the return stroke of the shaft may be achieved by weight of the work on the shaft, or by a spring or other suitable means (not shown).

The modified construction shown in FIG. 4 embodies all the parts heretofore described with the following exception: The flange 24 on shaft cap 23 may be replaced by a cone-shaped member 70 having a surface '71 inclined outwardly from right to left of FIG. 4. For this arrangement, the central opening 37 in switch base 36 is made slightly larger in diameter than shown in FIGS. 1 and 2.

From the foregoing it will be apparent that use of a cap press fitted on the reciprocable shaft not only makes it possible to use uniform sized shafts purchased in quantity, and to vary the lengths of such shafts, but also to vary the length of stroke of the shaft as desired. If a shorter stroke is desired, the flange on the cap is made longer and the switch is actuated sooner. If a shorter flange is used, it takes longer to reach the floating disc of the switch, resulting in a longer stroke. Substantial economy is acmeved by buying the precision shafts in quantity and employing piston caps which are made of cheaper, easily machined material so their lengths and the lengths of the flanges thereon can be varied economically.

The provision of a switch actuating surface, such as the annular surface 653 on the heating disc 55, completely surrounding the aperture in the disc, for contact by the circumferential flange 24, is an important feature of my invention. The construction of the shaft and switch herein described insure against bypassing of the switch, an occurrence not uncommon when contact between shaft and switch is confined to the movable switch contact point. In my construction, the entire floating disc 55 bears against the contact carrying blade 46 when the flange 24 bears against the annular surface 68 of the disc by direct axial thrust, thus positively insuring actuation of switch. The axial alignment of the switch with the shaft permits use of a larger and more dependable switch than is possible when the switch is located laterally of the shaft.

Changes may be made in details of construction and form of parts without departing from the scope of the invention as defined by the appended claims.

I claim:

1. An electrothermal actuator for imparting motion to mechanism located externally of the actuator comprising (a) a housing,

(1)) a shaft reciprocably mounted in the housing having a work-actuating free end portion adapted to project beyond the housing,

(c) means in the housing moving the shaft in axial direction to project beyond the housing into workactuati'ng position,

(d) electrical switch mechanism mounted in the housing having an opening between its sides axially aligned with and adapted for passage of the shaft therethrough, and

(e) means located circumferentially on the shaft between the shaft ends for engaging and actuating said switch mechanism when the work-actuating end portion of the shaft has passed through the switch mechanism beyond the housing into contact with the work.

2. The actuator defined by claim 1, in which the means located circumferentially on the shaft between the shaft ends for engaging the switch mechanism comprises a flange which extends continuously circumferentially around the shaft and engages an annular surface surrounding the opening in the switch mechanism when the workactuating end portion of the shaft has passed through the switch mechanism into contact with the work.

3. An electrothermal actuator for imparting motion to mechanism comprising (a) a housing,

(1)) a shaft reciprocably mounted in the housing having a work-actuating end portion adapted to project beyond the housing,

(0) means in the housing moving the shaft in axial direction into work-actuating position,

(d) electrical switch mechanism mounted in the housing having an opening between its sides axially aligned with and adapted for passage of the shaft therethrough, and

(e) means located circumferentially on the shaft between the shaft ends for engaging and actuating said switch mechanism when the work-actuating end portion of the shaft has passed through the switch mechanism into contact with the work, said last mentioned means comprising an elongated cap fitted over the work-actuating end portion of the shaft and a circumferential flange on the cap adjacent its inner end, said flange engaging an annular surface surrounding the opening in the switch mechanism when the workactuating end portion of the shaft has passed through the switch mechanism into work-actuating position.

4. The actuator defined by claim 1, in which the switch mechanism comprises a base, a fiXed contact on the base, a movable contact carrying blade mounted on the base, and a floating disc between the base and blade, and in which the means located circumferentially on the shaft for engaging said switch mechanism has annular contact with said floating disc and bodily moves said disc into Contact with the movable contact carrying blade when the work-actuating end portion of the shaft has passed through the switch mechanism into work-actuating position.

5. An actuator for imparting motion to mechanism comprising (a) a housing,

(b) a shaft reciprocably mounted in the housing,

(b-l) said shaft having a piston portion movable within the housing and a work-actuating end portion adapted to project beyond the housing, and

(c) an elongated cap press fitted on the workactuating end portion of the shaft in selected position,

(0-1) whereby a combined shaft and cap of variable predetermined length greater than the initial length of the shaft is produced.

6. An actuator for imparting motion to mechanism comprising (a) a high pressure housing,

(b) a shaft housing connected at one end to the high pressure housing,

(c) a shaft bearing and seal located in said shaft housing adjacent said high pressure housing,

(c-l) said housings having surfaces confining the bearing and seal axially and radially,

(d) a shaft reciprocably mounted in said shaft bearing having a piston portion in said high pressure housing and a work-actuating end portion adapted to project beyond the shaft housing, and

(e) a circumferential flange on the shaft located inwardly of its Work-actuating end,

(6-1) said flange bearing on a portion of the shaft housing located between the seal and said flange to limit the return stroke of the shaft into the high pressure housing.

7. An electrothermal actuator for imparting motion to mechanism comprising (a) a high pressure housing,

(b) a shaft housing connected at one end to the high pressure housing,

(c) a shaft bearing and seal located in said shaft housing adjacent said high pressure housing,

(c-l) said housings having surfaces confining the seal and bearing ain'ally and radially,

(d) a shaft reciprocably mounted in said shaft bearing having a piston portion in said high pressure housing and a work-actuating end portion adapted to project beyond the shaft housing,

(e) switch mechanism mounted in the outer end of the shaft housing having an opening between its sides axially aligned with and adapted for passage of the shaft therethrough, and

(f) a circumferential flange on the shaft located inwardly of its work-actuating end,

( 1"-1) said flange bearing on a portion of the shaft housing located between the seal and said flange to limit the return stroke of the shaft into the high pressure housing, and said flange engaging said switch mechanism to actuate the switch when the workactuating end portion of the shaft has passed through the switch mechanism into contact with the work.

8. The electrothermal actuator defined by claim 7, which includes an elongated cap mounted on the workactuating end portion of the shaft, and in which the circumferential flange on the shaft is mounted on the inner end of the cap.

9. The electrotherrnal actuator defined by claim 7, in which the switch mechanism comprises a base, a fixed contact on the base, a movable contact carrying blade mounted on the base, and a floating disc between the base and blade, and in which the circumferential flange on the shaft has annular contact with said floating disc and bodily moves said disc into contact with the movable contact carrying blade to separate said contacts when the work-actuating end portion of the shaft has passed through the switch mechanism into work-actuating position.

References Cited in the file of this patent UNITED STATES PATENTS 2,548,941 Brown Apr. 17, 1951 2,883,490 Larson Apr. 21, 1959 2,990,716 Butts July 4, 1961 

1. AN ELECTROTHERMAL ACTUATOR FOR IMPARTING MOTION TO MECHANISM LOCATED EXTERNALLY OF THE ACTUATOR COMPRISING (A) A HOUSING, (B) A SHAFT RECIPROCABLY MOUNTED IN THE HOUSING HAVING A WORK-ACTUATING FREE END PORTION ADAPTED TO PROJECT BEYOND THE HOUSING, (C) MEANS IN THE HOUSING MOVING THE SHAFT IN AXIAL DIRECTION TO PROJECT BEYOND THE HOUSING INTO WORKACTUATING POSITION, (D) ELECTRICAL SWITCH MECHANISM MOUNTED IN THE HOUSING HAVING AN OPENING BETWEEN ITS SIDES AXIALLY ALIGNED WITH AND ADAPTED FOR PASSAGE OF THE SHAFT THERETHROUGH, AND (E) MEANS LOCATED CIRCUMFERENTIALLY ON THE SHAFT BETWEEN THE SHAFT ENDS FOR ENGAGING AND ACUTATING SAID SWITCH MECHANISM WHEN THE WORK-ACTUATING END PORTION OF THE SHAFT HAS PASSED THROUGH THE SWITCH MECHANISM BEYOND THE HOUSING INTO CONTACT WITH THE WORK. 